Priority is claimed on Japanese Patent Application No. 2006-288565, filed Oct. 24, 2006, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a gas sensor.
2. Description of the Related Art
As an example of a conventional gas sensor which detects inflammable gas contained in an examination gas in a high temperature and high humidity environment, a gas sensor is known which is equipped with a heater unit for preventing a detection element from contacting with dew condensation, and thereby preventing producing the dew condensation inside the gas sensor (for example, refer to Japanese Unexamined Patent Application, First Publication No. H08-121754).
In addition, as another conventional gas sensor that is provided in an exhaust system on an oxygen electrode side of a solid polymer membrane fuel cell, and detects hydrogen gas leaked from a fuel electrode side to the oxygen electrode side through a solid polymer electrolyte membrane, a gas sensor is known which is equipped with a heater arranged between an inlet port for the examination gas and the detection element in order to heat the examination gas, and thereby prevents producing the dew condensation in the gas sensor (for example, refer to the specification of PCT Internal Publication No. WO03/042678).
In the above-mentioned conventional gas sensors, while stopping supplying electrical power to the gas sensor, the detection element is heated only by a heat transfer through an atmosphere around the detection element (i.e., the detection element is only heated by a radiation heat generated from the above-mentioned heater unit or the above-mentioned heater). Therefore, there is a case in which the predetermined necessary heating amount for preventing producing dew condensation inside the gas sensor is insufficient, and thereby causing the detection element contacting with the dew condensation. In such a situation, if the electrical power is supplied to the detection element, there may be a problem in which the temperature distribution on a surface of the detection element becomes locally uneven, and thereby causing defects such as destruction of the detection element, deteriorating the sensitivity of the detection element, and the like.
The present invention was made in view of the above-mentioned circumstances, and has an object of providing a gas sensor that can prevent the destruction of the detection element, deteriorating the sensitivity of the detection element, and the like, due to dew condensation.